Automotive outside mirror assemblies are automotive parts usually installed at both sides of an automobile right ahead of the two front doors to allow a driver to view the traffic conditions at both sides as well as at rear side of the automobile without the need of turning his neck.
Such an outside mirror assembly comprises in the housing thereof an adjustment mechanism that allows the driver in the cabin to control the mirror to direct upward/downward and/or leftward/rightward, and the mirror adjustment mechanism can be classified into a power drive type that requires a power supply and a manual drive type that is driven manually by a driver.
A power drive type mirror adjustment mechanism comprises a mirror position controller installed in the cabin, two driving motors each of which is electrically connected to the above position controller, two adjustment members each of which is geared with the corresponding driving motor via a transmission mechanism such as gear train to control position of the mirror, and sensors that sense position of the mirror while connected to a transmission mechanism between the driving motors and the adjustment members, and then, transmit signals of the sensed position to the mirror position controller.
Although the above power drive type mirror adjustment mechanism adjusts position of the mirror by moving the two adjustment members separately driven by power of the driving motors, there can be situations where the mirror needs to be adjusted manually. Thus, a power drive mirror adjustment mechanism shall preferably provide manual adjustment function in addition to its ability to correctly adjust position of the mirror by power driving.
Accordingly, a conventional power drive type mirror adjustment mechanism adopts a clutch structure that enables transmission of driving power of the driving motor to an adjustment member by frictional contact when the mirror adjustment mechanism is driven by power, and also enables manual adjustment of the mirror by generating a slip movement between the driving motor and the adjustment member when the mirror is adjusted manually.
A variety of such conventional clutch structures of a mirror adjustment mechanism have been suggested in ratchet type, rack and pinion type, etc.
Problems with the above ratchet type clutch structure are that it produces various operation noises and that its manual adjustability is strongly lowered as adjustments of the mirror position are made incrementally.
To overcome these drawbacks of the ratchet type clutch structures, rack and pinion type clutch structures have been introduced, which enable soft and easy adjustments of a mirror position with less noise when the mirror is adjusted manually.
A conventional rack and pinion type clutch structure comprises a clutch driving gear to be geared with specific gear train from the output axis of a driving motor, a pinion gear that comes in contact with one end of the clutch driving gear frictionally, an adjustment member including a rack gear that is geared with the pinion gear, and a spring member that provides frictional contact by endowing bias force in axial direction on contacting surface of the clutch driving gear with the pinion gear when the mirror is adjusted by power driving, and allows relative slip movements on contacting surface of the clutch driving gear with the pinion gear when the mirror is adjusted manually.
In such a rack and pinion clutch structure, frictional contact is generated on contacting surface of the clutch driving gear with the pinion gear by bias force of the spring member when the mirror is adjusted by power driving, and relative slip movements are generated on contacting surface of the clutch driving gear with the pinion gear as the pinion gear overcomes the frictional contact force (i.e. bias force in axial direction of the spring member) when the mirror is adjusted manually, as described above.
However, a problem with the conventional rack and pinion type clutch structure is that its adjustability at power drive is lowered due to insufficient power transmission at power driving. Since one side cross-section of the clutch driving gear and of the pinion gear are designed to contact each other in axial direction, the contacting surface generated hereby remains relatively small, and thus, frictional contact force generated on the contacting surface remains also small.
Another problem with the conventional rack and pinion type clutch structure is that this clutch structure requires various parts to be installed and large space because the clutch driving gear and the pinion gear are arranged in axial direction, and the installed structure thereof is complicated.
Consequently, this structure requires various parts to be installed in a relatively small space of the mirror adjustment mechanism, leading to the necessity of minimization and precision of the parts, whereby cost for manufacture of the parts arises and assembly of the parts becomes difficult.